The present invention is in the general field of organomagnesium compounds and relates in particular to dialkylmagnesium compounds and cyclopentadienyl magnesium compounds. The invention especially relates to di-n-hexylmagnesium and bis(cyclopentadienyl)magnesium.
Diorganomagnesium compounds are well known for their usefulness in a wide variety of chemical reactions. As reagents, these compounds can be used for the alkylation of ketones and the alkylation of metal halides or oxides to the corresponding metal alkyls. As catalysts, diorganomagnesium compounds are useful in the dimerization and polymerization of olefins, see Great Britain Pat. No. 1,251,177, the polymerization of epoxides, see U.S. Pat. No. 3,444,102, and the preparation of telomers, see U.S. Pat. No. 3,742,077. While they perform many of the same types of functions performed by Grignard reagents, diorganomagnesium compounds, owing to differences in electronic and steric factors, are more reactive than Grignard reagents toward certain types of compounds. In general, see also U.S. Pat. Nos. 3,646,231 and 3,822,219.
The utility of diorganomagnesium compounds is lessened by the fact that many are either solids or highly viscous liquids. This problem is generally overcome either by dissolving the compound in an inert hydrocarbon solvent (where possible) or by solvating the compound. All are unstable upon exposure to moisture and air and require handling under an inert atmosphere. Some diorganomagnesium compounds, with straight chain lower alkyl groups of up to four carbon atoms, are insoluble by themselves in hydrocarbon solvents and thus require solubilizing agents which will form a soluble complex. Examples of such solubilizing agents are alkyllithium compounds, see U.S. Pat. No. 3,742,077, dialkyl zinc compounds, see U.S. Pat. No. 3,444,102, alkali metal hydrides, see U.S. Pat. No. 3,655,790, and organoaluminum compounds, see U.S. Pat. Nos. 3,737,393 and 3,028,319, and combination of certain dialkylmagnesium compounds in hydrocarbon solvents. See U.S. Pat. Nos. 4,069,267 (C.sub.1 to C.sub.4 di-n-alkylmagnesium and C.sub.6 to C.sub.18 dialkylmagnesium), 4,127,507 (di-n-butylmagnesium and diethylmagnesium), 4,207,207 (dimethylmagnesium and di-n-butylmagnesium).
Processes for the preparation of dialkylmagnesium compounds are disclosed in U.S. Pat. No. 3,737,393. Processes for the preparation of bis(alkenyl)magnesium compounds are disclosed in U.S. Pat. No. 3,641,186.
U.S. Pat. Nos. 2,788,377 and 2,993,537 disclose the preparation of bis(cyclopentadienyl)magnesium or mixtures of bis(cyclopentadienyl)magnesium and bis(methyl-, or other lower alkylcyclopentadienyl)magnesium by direct reaction of cyclopentadiene or methylcyclopentadiene with metallic magnesium at high temperatures.
Dialkyl magnesium compounds have been prepared by the reaction of an alkyl halide with magnesium in an ether medium, followed by the addition of dioxane. Magnesium compounds obtained from such a process cannot be completely freed of ether. Since ether may have an adverse effect in certain applications for the dialkyl magnesium compounds, particularly as a catalyst component in Ziegler-Natta polymerization processes, such a process has major disadvantages.
When the foregoing reaction is conducted in an ether-free dispersion medium, such as in a hydrocarbon medium, the organomagnesium compounds are sometimes obtained as a precipitate having about the gross composition of organomagnesium halides. Such insoluble organomagnesium compounds are not only difficult to handle, but pose a number of problems for use in a polymerization process. Even when a dialkyl magnesium compound is prepared which is soluble in the hydrocarbon medium, the resulting solution is highly viscous, having a consistency similar to molasses in January.
The insolubility of the lower alkyl magnesium compounds makes preparation of them in a form free of undesirable co-product magnesium halides difficult. In particular the direct reaction of magnesium metal with an organic halide is disclosed in Glaze and Selman, Journal of Organometallic Chemistry, Vol. 5. p. 477 (1967), and W. N. Smith, Journal of Organometallic Chemistry, Vol. 64, p. 25 (1974). These articles deal with the preparation of diorganomagnesium compounds with straight chain alkyl groups of 5 carbon atoms and higher. Such compounds are soluble in hydrocarbon solvents and thus readily separable from the concurrently produced magnesium halide and unreacted magnesium.
In one process for making di-n-hexylmagnesium, magnesium powder and hexyl chloride are reacted in a hydrocarbon solvent in the presence of recycled di-n-hexylmagnesium as an activator. The reaction mixture is a viscous slurry of di-n-hexylmagnesium dissolved in hexane containing suspended magnesium powder and by-product magnesium chloride. The addition of a small amount of an aluminum compound such as diisobutylaluminum hydride, triethylaluminum or aluminum isopropoxide renders the solution more fluid or less viscous. The aluminum alkyl compound may also be added to the starting reaction mixture with similar viscosity reducing results. Although not wishing to be bound by any particular theory, it is believed that the aluminum compound causes partial depolymerization of long chains of associated magnesium dialkyls thus reducing viscosity. Since the magnesium product then contains a significant amount of aluminum, it is undesirable for some uses.
The basic reaction for preparing di-n-hexylmagnesium from an alkyl halide and magnesium is illustrated by the following equation: ##EQU1##
The di-n-hexylmagnesium is soluble in the hydrocarbon solvent, but the solution is extremely viscous. The magnesium chloride is a fine insoluble powder and is dispersed throughout the solution. Additionally, excess magnesium powder is dispersed in the solution. It is necessary to remove these solids from the magnesium alkyl product. The settling rate for such solids is extremely slow and consequently the viscosity remains high. Observation of untreated solution left standing for several days disclosed little or no settling. Heating of the solution provides some reduction in viscosity, but not enough for practical purposes. An additive is thus essential to provide a rapid settling rate and thereby increase the fluidity of such solution.
Accordingly there exists a need for an effective way of increasing the settling rate of solids formed on reacting alkyl halides with magnesium to form dialkylmagnesium compounds. Another desirable contribution would be a way of reducing the viscosity of normally viscous hydrocarbon solutions of dialkylmagnesium compounds without diluting the solutions to any significant extent, and without recourse to use of complexing ethers or the like. Still another desirable contribution would be a way of improving the solubility of dialkylmagnesium compounds in non-complexing solvents, especially in hydrocarbons.